Filter

ABSTRACT

The invention refers to a filter  1  with several rotating filter discs  3  mounted on a shaft  2  and which are provided with a porous filter medium. It is characterised by elastomer elements ( 8, 8 ′) being mounted on the shaft ( 2 ) as spacers between the individual filter discs ( 3 ). In addition, the invention refers to a filter disc  3  for a filter  1  of this kind.

[0001] The invention relates to a filter with several rotating filterdiscs mounted on a shaft and which are provided with a porous filtermedium.

[0002] A filter of this kind is known from AT 406936 (AT-A 155/99). Theproblematical aspect here is the fact that a large number of filterdiscs are used here on one shaft, which is supposed to overlap with thefilter discs of an additional shaft. In order to maintain flexibility inthe choice of disc supporting element and be able to use ceramicelements, for example, a frictional connection is recommended betweenshaft and disc. A sealing element must form the frictional connection.These circumstances entail the following risks and problems.

[0003] The manufacturing tolerances (disc, shaft and spacers) and theinfluence of the compressibility of the sealing elements can accumulate,with the result that the desired disc spacing can no longer be achieved.In extreme cases there may be damage due to the discs coming into directcontact with each other.

[0004] During start-up procedures in particular, there may be slippagedue to the inertia of the filter disc mass if the frictional connectionis inadequate. This leads to intensive wear on the sealing elements.

[0005] The aim of the invention is to permit reliable operations with asimple filter manufacturing process.

[0006] The invention is thus characterised by elastomer elements beingmounted on the shaft as spacers between the individual filter discs.Since elastomer elements are used as sealing material between theindividual filter discs and the centre core, there is no need for apositive-locking torque transfer between the discs and the centre cores.

[0007] An advantageous further development of the invention ischaracterised by the elastomer elements being manufactured in one piece.This permits manufacture at more reasonable cost, particularly if thespacing between the filter discs is narrow.

[0008] A favourable alternative further development of the invention ischaracterised by several elastomer spacers being provided, interspersedwith metal spacers. Better stability is achieved if these metal bushesare inserted, particularly if there is substantial spacing between thefilter discs.

[0009] An advantageous configuration of the invention is characterisedby several filter discs and elastomer elements being pre-loaded togetherin axial direction, where 5 to 20, preferably 10 to 15 filter discs canbe clamped together. Since the filter discs and elastomer elements arepre-loaded, this provides a simple seal between filter disc and centrecore and a good means of setting the spacing between the filter discs,while compensating any tolerances in the disc thickness arising duringmanufacture, compressibility of the sealing elements, etc. Since severalfilter discs can be pre-loaded together, any lack of uniformity can becompensated over a short stretch in each case and the problem of unevenspacing arising when all filter elements are linked from one side onlyis eliminated.

[0010] A favourable further development of the invention ischaracterised by several shafts with filter elements being arranged onone level and driven all together, by a belt for example. If the filterelements are arranged horizontally, for example, all shafts mountedconsecutively can be driven all together with only one drive, with thefilter discs rotating in opposite directions in the overlap area, thusimproving turbulence on the surface and providing a better cleaningeffect.

[0011] An advantageous configuration of the invention is characterisedby several levels of shafts with filter discs being provided, wherethese levels are separated from one other by dividing walls withsuitable openings mounted in a shared housing. In this way, severalpressure stages can be implemented in addition within one housing, withthe housing also being stabilised thanks to the dividing walls.Furthermore, a suitable flow pattern can be applied to avoidshort-circuit flow.

[0012] An advantageous further development of the invention ischaracterised by internal mountings being provided which are adapted tothe contours of the filter discs and which reduce the hollow space inthe housing. Due to these mountings, which extend into the wedgesbetween the filter discs, the free inner volume and the idle space aresubstantially reduced, which is a considerable advantage, particularlywhen increasing the concentration of the solids suspension in batchoperations.

[0013] A favourable configuration of the invention is characterised by afiltrate receiver being located at one end of the shafts and into whichall centre cores discharge, preferably also of pressure-resistantdesign. If this type of receiver is used, there is no need for therotary transmission leadthrough otherwise needed between centre core andpipe and which takes up a great deal of space. Due to thepressure-resistant design it is possible to apply overpressure forbackwashing, as well as underpressure, to increase the trans-membranepressure.

[0014] Another favourable further development of the invention ischaracterised by the raw medium being fed in at a tangent to the filterdiscs. Good cross-flow filtration is achieved with this flow control,without disturbing filtration on the discs near the inlet and alsoavoiding disc abrasion.

[0015] An advantageous configuration of the invention is characterisedby the shafts supporting the filter discs being speed-adjustable. Inthis way the turbulence between the filter discs can be adaptedaccordingly to the given requirements, particularly with changing mediumcomposition or substantial differences in concentration, without havingto change the entire flow-through path and/or the filtrate pressure.

[0016] An advantageous further development of the invention ischaracterised by a device being provided to run the filter up and downslowly at start-up and shutdown, where a motor with frequency converteror a turbo-coupling can be provided. As a result any slippage of thefilter discs can be avoided at start-up and shutdown. This is aparticular advantage with the friction connection due to the axialpre-loading with elastomer rings.

[0017] A further configuration of the invention is a filter disc for afilter according to the invention, characterised by a retaining bodybeing provided with a filter medium (wire, felt, foil membrane orsimilar) mounted on it. Thus a suitable base frame with acorrespondingly low-cost membrane foil can be provided to suit eachfilter application.

[0018] A favourable further development of the invention ischaracterised by the retaining body being made of perforated plate,sintered metal, ceramic, or porous synthetic material.

[0019] An advantageous configuration of the invention is characterisedby the foil membrane being of ceramic or polymer material.

[0020] A further development of the invention is characterised by thefilter medium being a wire, made by weaving synthetic or metal wires, ora screen, made by drilling holes in a plastic foil or a metal plate.

[0021] An advantageous further development of the invention ischaracterised by the foil membrane being welded or glued to theretaining body. As a result, suitable filter discs can be manufacturedat low cost.

[0022] A favourable configuration of the invention is characterised by abeaded edge being applied to the outer edge of the filter disc, made,for example, from elastic polymer material. This deflects the flow ofthe medium as it runs off the disc surface, thus avoiding disc abrasion.

[0023] A particularly favourable further development of the invention ischaracterised by the retaining body being cast, e.g. from ceramicmaterial, where the drainage channels are created by a core inserted inthe casting and which is eroded entirely by heat without leaving anyresidue behind. This method of manufacture permits simple and low-costmanufacture of the filter discs, where the one-piece filter disc typealso yields much longer service life in comparison with themanufacturing methods in several layers as used to date.

[0024] In the following the invention is described in examples based onthe drawings, where

[0025]FIG. 1 shows a state of the art filter,

[0026]FIG. 2 an illustration of the invention,

[0027]FIG. 3 a further illustration of the invention,

[0028]FIG. 4 a further representation of the invention,

[0029]FIG. 5 an arrangement of the shafts,

[0030]FIG. 6 a special design of the housing,

[0031]FIG. 7 a view of the filter,

[0032]FIG. 8 a filter disc according to the invention,

[0033]FIG. 9 a sectional view of a filter disc design according to theinvention, and

[0034]FIG. 10 a further design of a filter disc according to theinvention.

[0035]FIG. 1 shows a state of the art filtration module 1. Severalmembrane discs 3 are secured to each of the centre cores 2, 2′. Theliquid/suspension to be filtered is fed into a tank 4 through a pipe 5.A closed tank 4 is shown here. The tank can also be open, in which casethe membranes are submerged into the liquid. The membrane discs 3 have acylindrical cross-section here. The filtrate passes through the membraneinto the hollow disc body 3 and is guided to the centre of the disc aspermeate and then through the centre core 2, 2′ and through a pipe 6 outof the filter. The cleaned concentrate can be drained off later througha pipe 7. The membrane module 1 can be operated both with overpressureon the concentrate side and with underpressure on the permeate side.Correspondingly, the module 1 can be used as a closed casing or assubmerged membranes. The overpressure can be as high as 10 to 14 bar.

[0036] The membrane discs 3 may comprise inorganic elements, as well assupporting elements with a filter medium (wire, felt, polymer membrane).The design is suitable for both chemical cleaning of the filter medium,e.g. membranes in operation, as well as for fully automatic permeatebackwashing. The filtration modules 1 can be used for general filtrationprocesses for removal of solids, for microfiltration (as fromapproximately 0.3 microns), ultra-filtration, nano-filtration (up toapproximately 4000 Dalton) to reverse osmosis in drinking watertreatment, process water treatment, municipal and industrial waste watertreatment, as well as in product filtration, depending on the filtermedium used.

[0037]FIG. 2 provides a sectional view of a filter according to theinvention, where only one shaft 2 is shown with the individual filterdiscs 3. Elastomer elements 8, which serve as spacers, are mounted onthe centre core 2 between each of the individual filter discs 3. Thepresent illustration shows one-piece elastomer elements 8 as used tomaintain small spaces between the filter discs 3. This view also showsset collars with threaded pins 9, which are used to secure the filterdiscs 3 and elastomer elements 8 on the shaft 2.

[0038]FIG. 3 shows a variant of the spacers, where an elastomer element8′ is provided at each filter disc 3. The wider space between the filterdiscs 3 is obtained by a spacer 10, made preferably of metal, beinginserted between the corresponding elastomer elements 8′.

[0039]FIG. 4 shows the assembly of several filter discs 3 and elastomerelements 8, where set collars with threaded pins 9 are provided both atthe beginning and the end of a module of this type and hold the modules,comprising filter discs 3 and elastomer elements 8, or also theelastomer elements 8′ and metal spacers 10 between them, together underpre-load. As a result, it is easier to mount further modules and thefilter discs 3 are positioned with appropriate precision. This isparticularly important because the filter discs 3 of an additional shaft2′ should be positioned with more or less constant spacing and engagethe spaces between the discs without contact. Due to the overlap thusachieved, turbulence is generated which provides effective cleaning ofthe surfaces of the filter disc 3.

[0040]FIG. 5 shows a variant of the invention, where several shafts 2with filter discs 3 are arranged horizontally adjacent to one another,with two such levels one above the other. As a basic principle, it wouldbe possible to arrange several levels above one another. The levels areseparated inside the casing 11 by a dividing wall 12 with an opening 13.As a result, different concentrate stages with different pressure ratioscan be obtained for optimum efficiency with high concentrating effect inone casing. It is of advantage if the casing 11 is divided on thecentral axis of the shafts, which also facilitates assembly anddisassembly of the shafts using a crane. With this arrangement, theshafts 2 can be driven jointly for one level using a belt 14, 14′ withone single drive shaft 15. If the opening 13 in the dividing wall 12 ispositioned in a suitable location in relation to the suspension inletand outlet, short-circuit flow can be avoided. Thus, the desired outputcan also be achieved.

[0041]FIG. 6 shows a similar arrangement to FIG. 5, but with only onelevel of shafts 2. The additional internal mountings 16 to reduce thehollow space in the housing 11 are shown here, adapted to fit thecontours of the filter discs 3 and secured to the walls of the casing.In principle it would also be feasible to adapt the outer shape of thecasing to the contours of the filter discs, however this would makemanufacture of the casing more complicated.

[0042]FIG. 7 shows an assembled filter 1 with casing 11 and drive 17with drive shaft 15 and belt 14. In addition, the illustration shows theraw material feed 18 mounted at a tangent and the outlet 19. Thehorizontal centre cores 2 both discharge into a filtrate collecting tank20. This filtrate collecting tank 20 is of pressure-resistant design, sothat the suspension can also be fed in and discharged under pressure,which allows the filtration efficiency to be controlled by setting thecounter-pressure. If a vacuum is used, the maximum filtrate throughputsare higher. Furthermore, filtrate can be used for backwashing if higherpressure is applied. This improves cleaning of the surfaces and extendsthe intervals between chemical cleaning processes.

[0043] A filter disc 3 according to the invention is shown in FIG. 8.The disc has channels 21 and bars 22 on its centre level, so that theliquid filtered out of the suspension (filtrate) can be transported asrequired and then discharged into the centre core.

[0044] A filter medium, e.g. a membrane foil 23, can be applied to thesurface of the filter disc 3, as shown in FIG. 9. If the base frame 3 ismade of ceramic material and the membrane foil 23 also, it is anadvantage to sinter-fuse the two together. The filter medium, e.g.membrane, can also be attached by welding or gluing. In order tominimize abrasion on the disc, particularly in and around the outeredge, beading 24 made preferably of an elastic polymer material isapplied if abrasive media are to be processed. This beading 24 altersthe flow 25 of the medium as it runs off the filter disc 3 in such a wayas to prevent abrasion.

[0045] The filter disc 3 can be designed according to FIG. 10 at itsmiddle level. This figure once again shows the channels 21 and bars 22.In order to obtain this shape in a casting process, the inventionproposes that a core, e.g. made of wax or another organic material thatburns without leaving any residue, be formed, which has the same shapeas the channels and is inserted when the filter disc is cast. The futurechannels are then defined precisely by the shape of this core. Thefilter disc 3 is then burned and, during this process, the core burnsaway entirely leaving no residue, thus forming the channels. The shapeof the channels as shown is only one possibility, however other shapesalso allow favourable results. By using a core according to theinvention it is also possible to create other advantageous channelshapes that could not be produced otherwise. The core used need notnecessarily consist of one piece only, thus permitting further channelshapes.

[0046] The invention is not restricted by the configurationsillustrated.

1. Filter with several rotating filter discs mounted on a shaft andwhich are provided with a porous filter medium, characterised byelastomer elements (8, 8′) being mounted on the shaft (2) as spacersbetween the individual filter discs (3).
 2. Filter according to claim 1,characterised by the elastomer elements (8) being manufactured in onepiece.
 3. Filter according to claim 1 or 2, characterised by severalelastomer spacers (8′) being provided, interspersed with metal spacers(10).
 4. Filter according to one of claims 1 to 3, characterised byseveral filter discs (3) and elastomer elements (8, 8′) being pre-loadedtogether in axial direction.
 5. Filter according to claim 4,characterised by 5 to 20, preferably 10 to 15 filter discs (3) beingclamped together.
 6. Filter according to one of claims 1 to 5,characterised by several shafts (2) with filter discs (3) being arrangedon one level and driven all together, by a belt (14, 14′) for example.7. Filter according to claim 6, characterised by several levels ofshafts (2) with filter discs (3) being provided, where these levels areseparated from one other by dividing walls (12) with suitable openings(13) mounted in a shared housing (11).
 8. Filter according to claim 6 or7, characterised by internal mountings (16) being provided which areadapted to the contours of the filter discs (3) and which reduce thehollow space in the housing (11).
 9. Filter according to one of claims 1to 8, characterised by a filtrate receiver (20) being located at one endof the shafts (2) and into which all centre cores (2) discharge,preferably of pressure-resistant design.
 10. Filter according to one ofclaims 1 to 9, characterised by the raw medium being fed in (18) at atangent to the filter discs (3).
 11. Filter according to one of claims 1to 10, characterised by the shafts (2) supporting the filter discs (3)being speed-adjustable.
 12. Filter according to one of claims 1 to 11,characterised by a device being provided to run the filter (1) up anddown slowly at start-up and shutdown.
 13. Filter according to claim 11or 12, characterised by a motor (17) with frequency converter beingprovided.
 14. Filter according to claim 11 or 12, characterised by aturbo-coupling being provided.
 15. Filter disc for a filter according toone of claims 1 to 14, characterised by a retaining body being providedwith a filter medium mounted on it, preferably a wire or foil membrane.16. Filter disc according to claim 15, characterised by the retainingbody being made of perforated plate, sintered metal, ceramic, or poroussynthetic material.
 17. Filter disc according to claim 15 or 16,characterised by the foil membrane being of ceramic or polymer material.18. Filter disc according to one of claims 15 to 17, characterised bythe filter medium being a wire, made by weaving synthetic or metalwires, or a screen, made by drilling holes in a plastic foil or a metalplate.
 19. Filter disc according to one of claims 15 to 17,characterised by the filter medium e.g. the foil membrane, being weldedor glued to the retaining body.
 20. Filter disc according to one ofclaims 15 to 18, characterised by a beaded edge being applied to theouter edge of the filter disc (3), made, for example, from elasticpolymer material.
 21. Filter disc according to one of claims 15 to 19,characterised by the retaining body being cast, e.g. from ceramicmaterial, where the drainage channels are created by a core inserted inthe casting and which is eroded entirely by heat without leaving anyresidue behind.